Understanding Feline Leukemia in Cats
Feline leukemia virus (FeLV) stands as one of the most significant infectious diseases among domestic cats. Affecting between 2-3% of all cats in the United States and Canada, its impact is even greater in high-risk populations. FeLV is a retrovirus exclusive to felines—it doesn't infect humans, dogs, or any other species.
How FeLV Spreads
The virus is highly contagious among cats. Transmission occurs mainly through saliva during close contact—think mutual grooming, bite wounds, or sharing feeding dishes and litter boxes. Less commonly, it's present in urine and feces. Infected mother cats can pass it to kittens before birth or while nursing. However, FeLV doesn't last long outside a cat's body, so prolonged direct contact is usually needed for infection.
- Cats living with infected or untested companions
- Free-roaming outdoor cats
- Cats from shelters, catteries, or multi-cat households
Kittens and young adults are especially vulnerable because resistance increases with age. Blood transfusions from infected donors and crowded environments also raise risk.
What Happens After Exposure?
Cats exposed to FeLV may experience several outcomes:
- Abortive infection: The cat's immune system eliminates the virus entirely; these rare cases result in immunity without contagiousness or symptoms.
- Regressive infection: The virus hides in body compartments like bone marrow. It's not found in blood nor shed to others but could reactivate if immunity drops (about 10-30% of cases).
- Progressive infection: The virus persists in the bloodstream; these cats shed FeLV and are likely to develop related diseases such as cancer or immune suppression—most fatal cases fall here.
Symptoms and Clinical Signs
The signs of FeLV are unpredictable—some cats show no symptoms for weeks, months, or even years after infection. Over time, you might notice:
- Poor appetite and weight loss
- Dull coat condition
- Pale or yellow gums
- Lethargy or persistent fever
- Enlarged lymph nodes
- Mouth inflammation (stomatitis/gingivitis)
- Frequent infections (skin, bladder, respiratory)
- Anemia or reproductive failures
Cancer (especially lymphoma) and neurological problems can also occur. Because FeLV suppresses the immune system, secondary infections are common.
Diagnosing Feline Leukemia
Your veterinarian will use several tests to diagnose FeLV:
- The ELISA test: Detects viral antigens in blood; used for early screening.
- The IFA test: Confirms infection by identifying the virus within white blood cells/platelets; typically positive only later on.
- The PCR test: Finds viral DNA integrated into the cat’s genome—even if not actively replicating—which helps clarify regressive infections.
No single test at one time is definitive for stage; sometimes retesting after weeks is necessary to distinguish between transient, regressive, or progressive infection.
Treatment Options for FeLV-Positive Cats
No cure exists for feline leukemia. Treatments focus on managing complications—antibiotics for secondary infections, blood transfusions for anemia, chemotherapy for cancer, and immune-modulating drugs when appropriate. Good nutrition and regular veterinary check-ups are crucial. Some infected cats live comfortably for months or years with attentive care; however, prognosis is less favorable for those with progressive infections (median survival: 2.5–3 years post-diagnosis).
Prevention: The Best Strategy
- Keep your cat indoors to minimize exposure risks.
- Avoid sharing food/water bowls and litter boxes between healthy and infected cats.
- Test all new arrivals before introducing them to multi-cat homes.
- Spay/neuter to reduce risky behaviors like fighting.
The FeLV vaccine, considered core for kittens and recommended for at-risk adults, should only be given to FeLV-negative cats—it can't clear existing infections. Even vaccinated cats should be tested after exposure since no vaccine offers complete protection.
Caring for an Infected Cat at Home
- Monitor weight loss and appetite changes closely.
- Watch for signs of secondary infections (sneezing, lethargy).
If your cat tests positive: keep them indoors both to protect other felines and reduce their own risk of secondary illnesses. Promptly address any health changes with your vet's help.
A Note on Contagion Across Species
You don't need to worry about transmission outside the feline world—FeLV isn't contagious to people or other pets like dogs. Thanks to modern testing and vaccination strategies, prevalence has dropped dramatically in North America—but vigilance remains key for all cat owners.
